This invention relates to a method for the preparation of substituted ether phthalic anhydrides. The products are useful chemical intermediates for the further preparation of various compounds such as the corresponding di-carboxylic acids and the various derivatives thereof, including for example, the salts, esters, acyl halides, amides, imides and the like. The ether phthalic anhydrides are useful as curing agents for epoxy resins and the like, and as monomers in the preparation of polyesters, for example by polycondensation with a suitable dihydric alcohol.
Various methods for the preparation of ether phthalic anhydrides have been described in the chemical literature. The preparation of diether-diphthalic anhydrides by formation of the diether di-o-xylyl groups followed by oxidation to the diether diphthalic anhydride is disclosed by Koton et al, Zh. Org. Khim. 4, 774 (1968); and Zh. Org. Khim. 6, 88 (1970).
Myers (U.S. Pat. No. 3,965,125) teaches the preparation of halogenated phthalimides from halogenated phthalic anhydride and reaction of the phthalimide with an alkaline metal salt of a phenol or a diphenol to form the bis-ether imide which is then hydrolyzed, acidified, and dehydrated to the bis-ether phthalic anhydride.
Heath et al (U.S. Pat. No. 3,956,320) disclose the preparation of aromatic bis(ether anhydride) by reaction of a nitro-substituted phenyl dinitrile with a metal salt of a dihydroxy aryl compound in the absence of a dipolar aprotic solvent and conversion of the resultant aryloxy tetranitrile to the tetra-acid followed by dehydration to the aryloxy dianhydride. Thus, for example, the patentees disclose the reaction of hydroquinone with 4-nitrophthalonitrile in the presence of potassium carbonate, followed by hydrolysis, acidification and dehydration to form the hydroquinone di-ether phthalic anhydride.
Johnson et al (U.S. Pat. No. 4,020,069) teach the reaction of a 4-nitro-N-alkyl phthalimide and an aromatic dihydroxy compound in the presence of potassium carbonate and dimethyl sulfoxide followed by hydrolysis to form a bis-ether dicarboxylic acid which may then be dehydrated to form the aromatic ether dianhydride.
Williams (U.S. Pat. No. 3,850,965) discloses a method for the preparation of aromatic ether anhydrides by reaction of a nitro- or halo-substituted aromatic anhydride with an alkali phenoxide. Thus, for example, sodium phenoxide was reacted with 3-fluorophthalic anhydride in anhydrous dimethylformamide to form 3-phenoxyphthalic anhydride.
Heath et al (U.S. Pat. No. 3,787,475) disclose the preparation of aryloxy phthalic acids by reaction of a metal phenolate such as sodium phenolate and a nitro ester of a phthalic acid such as diethyl-4-nitrophthalate or a corresponding nitrophthalonitrile, followed by hydrolysis of the ester group or cyano group. The resulting substituted phthalic acid may then be converted to the anhydride.
Williams (U.S. Pat. No. 3,850,964) discloses a method for making aromatic bis(ether anhydrides) by reaction of alkali metal diphenoxides with halo- or nitro-substituted aromatic anhydrides. Thus, for example, a sodium salt of 4,4'-dihydroxy biphenol was reacted with 3-fluorophthalic anhydride in anhydrous dimethyl formamide to form 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride.
Markezich (U.S. Pat. No. 3,992,407) discloses the preparation of aromatic bisimides by reaction of a 3- or 4-fluoro-N-substituted phthalimide with an aromatic dihydroxy compound in the presence of a solid alkali metal fluoride, such as potassium fluoride, using a dipolar aprotic solvent.